Hitherto, as a heating apparatus of this type, for example, the food thawing cooking oven as disclosed in Japanese Patent Publication No. 55-51541 has been known. FIG. 5 shows its constitution, in which an agitator 3 is provided in a ceiling 2 of an oven 1 which can be enclosed tightly, and a magnetron irradiation unit 4 is disposed nearby. A detachable food rack 5 is provided in the oven 1, a liquid pan 6 for feeding water or oil is disposed beneath, and a heater 7 by gas or electric heating is disposed further beneath. By the combination of magnetron irradiation unit 4, liquid pan 6, and heater 7, both heating by magnetron irradiation from above and steam heating by boiling water from beneath can be combined.
When heating the food by such constitution, combination of internal heating by magnetron irradiation and steam heating by steam can be selected corresponding to the cooking menu. Besides, since steam is generated, as described therein, it can be applied in thawing of frozen bread and frozen cake, or as bread and cake cooker in whole process of fermentation and baking.
In such conventional heating apparatus, however, when water is contained in the liquid pan, the steam will not exceed the boiling point (100.degree. C. at atmospheric pressure), and it is the steam below the saturation temperature that is supplied into the heating chamber. Such steam damps the food surface. In particular, when the food is frozen, an extreme dew condensation occurs on the food surface in unthawed state. Accordingly, when frozen bread or the like is thawed, drying of the food is prevented, but the crust which is desired to be crisp becomes wet and sticky, and the touch is significantly spoiled.